First-degree relatives of patients with type I (early-onset, insulin-dependent) diabetes are considered at higher risk than the general population for the development of diabetes. This study aims to identify individuals at moderate to high risk for developing type I diabetes and to examine interventions that might prevent the development of diabetes. The test designed to identify those at risk for the development of diabetes is the detection of antibodies directed against the pancreatic islet cells, the cells within the pancreas responsible for producing insulin. Individuals with high titer antibodies will be tested for their ability to release insulin, and those with abnormal test results will then be given either a placebo or small amounts of insulin. The insulin injections are aimed at inducing immunologic tolerance, and thus preventing further disruption of islet cells.